Thermoelectric cross-plane properties on p- and n-Ge/SixGe1-x superlattices

Silicon and germanium materials have demonstrated an increasing attraction for energy harvesting, due to their sustainability and integrability with complementary metal oxide semiconductor and micro-electro-mechanical-system technology. The thermoelectric efficiencies for these materials, however, are very poor at room temperature and so it is necessary to engineer them in order to compete with telluride based materials, which have demonstrated at room temperature the highest performances in literature [1]. Micro-fabricated devices consisting of mesa structures with integrated heaters, thermometers and Ohmic contacts were used to extract the cross-plane values of the Seebeck coefficient and the thermal conductivity from p- and n-Ge/SixGe1-x superlattices. A second device consisting in a modified circular transfer line method structure was used to extract the electrical conductivity of the materials. A range of p-Ge/Si0.5Ge0.5 superlattices with different doping levels was investigated in detail to determine the role of the doping density in dictating the thermoelectric properties. A second set of n-Ge/Si0.3Ge0.7 superlattices was fabricated to study the impact that quantum well thickness might have on the two thermoelectric figures of merit, and also to demonstrate a further reduction of the thermal conductivity by scattering phonons at different wavelengths. This technique has demonstrated to lower the thermal conductivity by a 25% by adding different barrier thicknesses per period

CMOS analog-digital circuit components for low power applications

Dissertação de mestrado em Micro and NanoelectronicsThis dissertation presents a study in the area of mixed analog/digital CMOS power extraction circuits for energy harvester. The main contribution of this work is the realization of low power consumption and high efficient circuit components employable in a management circuit for piezoelectricbased energy harvester. This thesis focuses on the development of current references and operational amplifiers addressing low power demands. A brief literature review is conducted on the components necessary for the power extraction circuit, including introduction to CMOS technology design and research of known low power circuits. It is presented with multiple implementations for voltage and current references, as well for operational amplifier designs. A self-biased current reference, capable of driving the remaining harvesting circuit, is designed and verified. A novel operational amplifier is proposed by the use of a minimum current selector circuit topology. It is a three-stage amplifier with an AB class output stage, comprised by a translinear circuit. The circuit is designed, taking into consideration noise reduction. The circuit components are designed based on the 0.35mm CMOS technology. A physical layout is developed for fabrication purposes. This technology was chosen with consideration of robustness, costliness and performance. The current reference is capable of outputting a stable 12nA current, which may remain stable in a broad range of power supply voltages with a minimum voltage of 1.6V. The operational amplifier operates correctly at voltages as low as 1.5V. The amplifier power consumption is extremely low, around 8mW, with an optimal quiescent current and minimum current preservation in the output stage.A principal contribuição desta dissertação é a implementação de circuitos integrados de muito baixo consumo e alta eficiência, prontos a ser implementados num circuito de extração de energia com base num elemento piezoelétrico. Esta tese foca-se no desenvolvimento de um circuito de referência de corrente e um amplificador operacional com baixa exigência de consumo. Uma revisão da literatura é realizada, incluindo introdução à tecnologia Complementary Metal-Oxide-Semiconductor (CMOS), e implementação de conhecidos circuitos de baixo consumo. Várias implementações de referência de tensão e corrente são consideradas, e amplificadores operacionais também. Uma referência de corrente auto polarizada com extremo baixo consumo é desenvolvida e verificada. Um amplificador operacional original é proposto com uma topologia de seleção de corrente mínima. Este circuito é constituído por três estágios, com um estágio de saída de classe AB, e um circuito translinear. O circuito tem em consideração redução de ruído na sua implementação. Os circuitos são desenvolvidos com base na tecnologia 0.35mm CMOS. Uma layout foi também desenhada com o propósito de fabricação. A tecnologia foi escolhida tendo em conta o seu custo versus desempenho. A referência de corrente produz uma corrente de 12nA, permanecendo estável para tensões de alimentação de variáveis, com uma tensão mínima de 1.6V. O circuito mostra um coeficiente de temperatura satisfatório. O amplificador operacional funciona com tensão de alimentação mínima de 1.5V, com um consumo baixo de 8mW, com uma corrente mínima mantida no estágio de saída

Current Protection for the Energy Harvesting from Exercise Machines (EHFEM) Project

The Energy Harvesting from Exercise Machines (EHFEM) project intends to create an exercise machine that recycles the energy expended by an athlete operating the machine by sending it to the electric grid. The work done by the user goes through a DC-DC converter and an inverter in order to prepare it for delivery to the grid. A protection circuit ensures that the inverter does not try to pull too much current from the DC-DC converter. The project implements a current protection system that ensures the system doesn’t experience an overcurrent condition

Energy challenges for ICT

The energy consumption from the expanding use of information and communications technology (ICT) is unsustainable with present drivers, and it will impact heavily on the future climate change. However, ICT devices have the potential to contribute signi - cantly to the reduction of CO2 emission and enhance resource e ciency in other sectors, e.g., transportation (through intelligent transportation and advanced driver assistance systems and self-driving vehicles), heating (through smart building control), and manu- facturing (through digital automation based on smart autonomous sensors). To address the energy sustainability of ICT and capture the full potential of ICT in resource e - ciency, a multidisciplinary ICT-energy community needs to be brought together cover- ing devices, microarchitectures, ultra large-scale integration (ULSI), high-performance computing (HPC), energy harvesting, energy storage, system design, embedded sys- tems, e cient electronics, static analysis, and computation. In this chapter, we introduce challenges and opportunities in this emerging eld and a common framework to strive towards energy-sustainable ICT

Protection System For the Energy Harvesting from Exercise Machines (EHFEM) Project

The goal of the Energy Harvesting from Exercise Machines (EHFEM) project seeks to harness the energy generated by people using exercise machines and deliver this energy to the electric grid [1]. The implementation consists of a protection system, DC-DC converter, and an inverter. This project involves redesigning the existing DC-DC input protection circuit and current limiter for the EHFEM project [2]. The DC-DC converter takes in the power from the exercise machines and converts it to a manageable voltage level for the inverter. Due to a problem where the inverter may overload the converter, a current limiter sets to limit the current between the two circuits [4]. The inverter demanding more current at a lower voltage than the DC-DC converter can provide causes this overload. The input protection circuit for the DC-DC converter presents another major component of the protection system. The DC-DC converter must operate within set input voltage and current parameters. Concurrent with this project, students Byung Yoo and Sheldon Chu have developed a new DC-DC converter design with an operational range of 6 V to 51 V [7]. This paper proposes a design for an overvoltage protection circuit to limit the input of Yoo’s and Chu’s DC-DC converter to within its operational range. The input protection circuit regulates the incoming voltage from the elliptical machine and filters out any high frequency transient responses with capacitive filtering to generate a smooth DC signal. The circuit also functions to divert excess voltage and current that accumulates during the Enphase Micro-inverter’s startup period where an open load appears across the DC-DC converter leading to an overvoltage level [3]. A current sense circuit ensures the output from the DC-DC converter to the inverter delivers only as much power as the inverter can convert [4]. The device maintains a minimal component count number and lacks any excessively large components permitting easy assembly and installation. The device operates with a minimal loss of energy and minimizes fabrication costs allowing for recuperation of initial production costs over 10 years of normal use

IMPLEMENTATION OF THERMOELECTRIC GENERATOR MODULE AS EXTERNAL ENERGY SOURCE TO RFID TAG

One of the wireless technologies available that are expanding very fast is the RFID technology. There are three (3) different types such as active, passive and semi-active RFID tag. The main concern is that the tag consumes vast amount of power due to the availability of sensors and internal electronic components in the circuitry of the tag. The goal of this project is to solve this matter by finding suitable approach for supplying power externally to the tag. At present RFID tag uses battery to operate and this battery does not last long due to low capacity. From the literature review and detailed research, it is found that the Thermoelectric Generator (TEG) is the best approach to be implemented to solve the issue. TEG is used to harvest heat energy from human body and convert it to electrical energy and directly supply to the tag. Other option such as the replacement of normal battery to rechargeable battery is also in consideration. This will enable a cutting cost of maintenance of the tag. It also shall increase the performance of the active RFID tag